Our local ISD also has the zero tolerance policy and would not allow t-shirts with weapons pictured on them, for any reason.
Even though he taught in public school, Dad always believed uniforms were the way to go and said so whenever student or teacher clothing was the topic.
Our homeschool Enrichment Classes dress code includes no tank tops, no short dresses/skirts/shorts (4 inches above the knee or longer). Shorts were not allowed at all until the exercise classes were complaining about not having enough time to change clothes. Weightlifting participants had to wear pants (athletic clothing) below the knee, but now can wear shorts. NRA t-shirts are okay, though.
Side note:
Shooting sports is one of the most success programs we have. One of "ours" competes in NRA and has been Junior Olympic champion.